Soulburn Studios Art Lessons

Wet Looking Materials
By Neil Blevins
Created On: June 11th 2002
Updated On: Sept 25th 2005

What makes a material look wet? Or gooey, for those of you who love to make slimy creatures. Well, first, lets look at the problem at the most basic level. An object looks wet because the surface of the object has a thin sheet of water over top of it. So what makes water look like water?

Water has no obvious diffuse component.
It has a strong specular component (specular reflection), especially at glancing angles due to the fresnel equation.
It is also refractive, however since the sheet of wetness is so thin, the only visual indication of refraction usually manifests itself as a darkening of the surface. In hard surfaces like a rock, this is due to internal reflections between the water surface and the rock surface, which dims the light reflected back to the eye. In porous surfaces like cloth, a similar phenomena is happening, the surface absorbs water, so when the surface is struck by light the light scatters deeper into the material, and so hits more particles before leaving the cloth. Each particle absorbs a slight amount of the light, so when the light emerges from the material back to the eye, the surface appears darker because more of the light is absorbed in the material.

So the main two features of a wet surface vs a dry surface is a darker color and a strong specular highlight.

If you look at these rocks, you can see the diffuse component of the rock, and over top you can see nice sharp specular reflections of its environment (slightly distorted by the bumps on the rock). Since this rock in its natural state would have almost no specular reflections, the viewer, upon seeing the rock, would assume it to be wet. It's always easier to make something look wet if the object has no specular component to begin with.

Although I have no photo of a dry rock, you'd find the dry rock to have a slightly lighter color than the rocks in the photos above.

Here's another example image, this is a carrot, half of which is wet, and half of which is dry. Notice the differences in the wet and dry sides, the surface has a strong specular highlight (a reflection of the nearby window) and the color is slightly darker and more saturated.

Wet Carrot

Using Highlights To Make Something Look Wet

As discussed in previous tutorials, a specular reflection can be either a true reflection of your environment (either an environment map or raytraced reflections), or a cheat such as a blinn or phong highlight. If your object just needs to look wet, and you don't need accurate reflections, you might be able to get away with a blinn highlight. Water is very reflective and it's surface is quite smooth (unless being perturbed by waves or by a strong bump on the surface it's sitting on), hence any blinn highlight should be strong and sharp. So if your original shader has no highlight, just add a strong and sharp highlight to it as the first step in making the surface look wet.

For these following examples, I'm using 3DStudio MAX, but the same theory applies to all major software packages.

But what happens if your surface already has a highlight?

Well, one thing you can do inside 3DStudio MAX is apply a Shellac material to your object. Shellac lets you apply a second material to your first material in an additive fashion. So whatever exists in your second material will be added to your first material. It's great for layering highlights.

So for example, start with your original material. Make a Shellac material, and place your original material into slot1. Inside of slot2 place a new standard material, call it Highlight. This will be our Highlight material.

Now lets tweak our Highlight material a bit. Go into your Highlight material, change the diffuse color to black, we don't want a diffuse component, we're just after the highlight. Now adjust the highlight to your liking.

Go back up your material chain to the Shellac and adjust the shellac value to something between 100-200%.

Another note about, if your material has a displacement map, and you place it inside a Shellac material, the displacement map won't work. This is a limitation of the Shellac material. If this is the case, try placing your Shellac material inside Blur's Utility Material, available here. And place your displacement map in the Utility Material, this will bring your displacement back.

One last thing to note, if using a shellac, the Highlight material will not be affected by the bump map from your slot 1 material. This can be useful in some situations, like with a coat of varnish on wood, the varnish would usually not inherit the bump from the wood, but have it's own type of bump. But in the case of a thin sheet of water, the bump map on your original material should probably affect the highlight of the Highlight material, so place in the bump map slot of the Highlight material the same bump map that's affecting your material in slot 1. Maybe reduce the Highlight material's bump map's intensity slightly, depending on how the effect looks. Now apply the shellac material to your object.

Wet Example

Here's a max file that made the image above, max5: wet_sphere_01.zip

Another thing to try, instead of using another Standard Material in your second slot, you may want to use Blur's HighlightOnly Material, available here. This is a material that does what you'd expect, it's a highlight only, with no diffuse component, and works great in shellacs.

Another shader to try is the Multi-Layer shader which has two highlight built in, so your first highlight can be your original highlight and the second highlight can be the one simulating the wet look.

Now that the highlight is taken care of, make sure your object is slightly darker and more saturated than your dry material, and your illusion of a wet material is complete.

Using Reflections To Make Something Look Wet

Here's a real world example of a situation where you may wish to do a real raytraced reflection or use a reflection map instead of just a blinn highlight. This is some smooth seaweed I found on the beach:

Seaweed Reflections

Notice the reflections of the sun, sky and ground on the wet surface. To get this look you'll probably want to do either real raytraced reflections, or use an environment map. Here's my max example above but with an environment map instead of just the specular reflection...

Wet Example 2

Here's a max file that made the image above, max5: wet_sphere_02.zip